1. Field of the Invention
The present invention relates to novel thermally stable polymers produced from bisimides.
2. Description of the Prior Art
Polymers produced by reacting an N,N'-bisimide of an unsaturated dicarboxylic acid such as, for example, an N,N'-bismaleimide, with a diprimary diamine are described in French Patent No. 1,555,564. The quantities of N,N'-bisimide and of diamine are selected such that the ratio: ##EQU1## is at least equal to 1, and preferably is less than 50. Thermally stable resins are thus produced which withstand severe thermal stresses remarkably well.
The above-mentioned French patent also discloses that the resins may be prepared in bulk by heating intimate admixture of the reactants. These resins may also be prepared in an inert polar diluent such as dimethylformamide, N-methylpyrrolidone or dimethylacetamide. The latter process is the preferred, when the end application of the polymer requires it to be in solution form.
For many uses, the noted '564 French patent indicates that a two-step process is advantageous. In a first stage, a prepolymer is prepared by heating the intimate admixture of the two reactants to a temperature on the order of 100.degree. to 250.degree. C. The prepolymer thus produced may be employed in solution, suspension or powder form, or else may simply be shaped by casting while in hot state. In a second stage, curing of the prepolymer is effected by heating it to temperatures on the order of 300.degree. C., under pressure if desired.
These polymers may be converted into films or into polycellular materials. They are of very special interest for the preparation of molded shaped articles, in combination, if desired, with fibrous or powdered fillers or laminates based on inorganic fibers (single fibers, fiber cloth or nonwovens) such as, for example, carbon, boron or glass fibers. However, the preparation and use of such polymers require strict precautions to be observed for reasons of health and hygiene when the diprimary diamine is aromatic in nature, because of the toxicity associated with certain of such aromatic diamines.